This invention relates to the production of particulate compositions containing active ingredients, for instance agriculturally useful active ingredients such as insecticide or herbicides or biologically active ingredients such as enzymes. The invention includes relatively coarse particles that can be handled as powders and fine particulate compositions which are generally in the form of liquid dispersions of the fine particles. Numerous ways of protecting active ingredients from the ambient environment are known. Some rely on a wholly liquid system. In U.S. Pat. No. 4,801,544, aqueous micelles of enzyme and surfactant are emulsified into a hydrocarbon solvent. In U.S. Pat. No. 4,906,396, enzyme is dispersed in a hydrophobic fluid, such as a silicone oil.
More usually, the enzyme is protected by a solid phase. In U.S. Pat. No. 4,090,973 solid surfactant is used. Often, however, a polymeric material is used. The enzyme or active ingredient may be dispersed in a polymeric matrix or it may be encapsulated by a polymeric shell formed around a core containing the active ingredient.
The solid polymeric material can be made by polymerisation of monomeric material in the presence of the active ingredient, but this is generally undesirable and normally the solid polymer of the matrix or shell is formed by depositing solid polymer from a solution of polymer. The polymer can remain chemically unchanged during the deposition from dissolved to solid form, the deposition being due primarily to a change in the solvent composition or properties. Alternatively, deposition can be caused by, accompanied by or followed by a chemical change in the polymer, such as neutralisation, complexing with another polymer, or cross linking. The formation of a solid polymer shell in this manner from a solution of polymeric material is generally termed coacervation.
Typical techniques for forming a polymer shell are described in, for instance, GB 1,275,712, 1,475,229 and 1,507,739, DE 3,545,803 and U.S. Pat. No. 3,591,090.
A particular problem arises when the active ingredient is an enzyme, especially an enzyme suitable for incorporation in detergents, because of the difficulty of preventing the enzyme losing activity before use.
Many different ways of encapsulating enzymes have been proposed. Some do not include coacervation. For instance GB 1,377,725 contacts atomised droplets of an aqueous slurry of enzyme with particles of starch. However there is a risk that the resultant coating will be discontinuous. It is therefore preferred to form the coating or matrix by deposition of solid polymer from a solution of polymer in which the enzyme is dispersed, i.e. by coacervation.
For instance in U.S. Pat. No. 3,838,007 droplets of enzyme dispersed in an aqueous solution of, for instance, gelatin are dispersed into water and then cross linked, to give cross linked particles of the gelatin containing the enzyme.
In JP-A-61254244 a typical process comprises mixing enzyme powder and silica into an aqueous solution of polyvinyl alcohol or other suitable polymer, dispersing the aqueous suspension into a non-aqueous liquid and adding acetone, so as to deposit the polymer as a wall around the enzyme particles. The product is said to have a particle size of around 50 to 2,000 um.
In U.S. Pat. No. 4,898,781 a dispersion is formed of enzyme powder in propylene glycol and aqueous polyvinyl alcohol and this dispersion is then converted into particles by various techniques. In one technique, the dispersion is introduced as droplets into an aqueous solution of cross linking agent, thereby solidifying by cross linking the polyvinyl alcohol. In another technique, the dispersion is dispersed into a hydrophobic solvent and then heated, so as to drive off water and solidify the polyvinyl alcohol. The products are said to have a size of 20 to 1,000 .mu.m. Other techniques are described. JP-A-63105098 includes similar process description and many of the examples are identical. It proposed that the particles of enzyme in a covering of polyvinyl alcohol should be homogeneously dispersed in a liquid or gel detergent.
U.S. Pat. No. 5,035,900 describes processes for encapsulating enzyme or other biologically produced material in a matrix of polymeric material by mixing the polymeric material with an aqueous liquor containing the biologically produced material (as a fermentation liquor or plant extract), dispersing this mixture in a water immiscible liquid and azeotroping the dispersion. The product can either be relatively coarse beads that can be recovered or a stable dispersion of small particles in the water immiscible liquid. Although this is a very useful recovery technique and provides some protection to the enzyme, additional stabilisation is desirable.
Instead of or in addition to protecting the active ingredient from the environment, there is also a need to provide a convenient way of delivering the active ingredient to a chosen place for use, especially when the active ingredient may be toxic and/or may need to be released into the environment only at a controlled rate.
For instance when the active ingredient may have some toxicity (for instance when it is a water insoluble pesticide or other agrochemical) it is frequently necessary to formulate the compound as a concentrate that can be diluted at the point of use to form a sprayable composition. When the compound is water soluble, the concentrate can be a concentrated aqueous solution or a water soluble granule or other soluble solid. However many agriculturally useful compounds are insoluble in water. It is generally preferred that they should be applied by spraying an aqueous composition and so the concentrate of water-insoluble active ingredient must be stable and must be capable of easy distribution into water.
One common type is a wettable powder in which powdered insoluble material has been treated to render it wettable, but there is increasing concern about dusting and other environmental problems associated with traditional wettable powders.
Another type is a dispersible paste or cream, usually referred to as a "flowable". This can readily be diluted with water and is reasonably satisfactory for many active ingredients. However a problem with both flowables and wettable powders is that the active ingredient has to be produced in the form of particles of a desired small size and this can be difficult or impossible with some materials, especially some agrochemicals. For instance these formulations are not appropriate when the active ingredient is a liquid or when it is a relatively low melting solid, for instance a solid that melts at below 80.degree. C., because of the difficulty of making the active ingredient in this fine particulate form.
Water insoluble liquids and low melting solids can be formulated as emulsifiable concentrates but it is now frequently considered desirable to avoid this type of formulation for environmental reasons associated with, for instance, the organic solvent that is generally present in such concentrates.
It would therefore be desirable to be able to provide an active ingredient in the form of a particulate composition which is readily dilutable by water, is substantially free of organic solvent or dusting problems, and gives a satisfactory rate of release of the active ingredient.
It is already well known to use polymeric materials in the formulation of various active ingredients. Thus it is known to diffuse a low melting or liquid active ingredient into a preformed polymeric matrix (e.g., as in U.S. Pat. No. 4,303,642) or to encapsulate an active ingredient in beads by forming an emulsion or dispersion in water of polymerisable material and the active ingredient and then polymerising the polymerisable material. The product will, depending upon the materials and process conditions, be in the form of either a particulate matrix throughout which the active ingredient is distributed or small (or large) capsules comprising a shell of polymeric material around a core containing the active ingredient.
Although these diffusion and polymerisation techniques are useful in some instances, they are relatively expensive and this is justified only because they are designed primarily to provide controlled release of an active ingredient. They are not appropriate to the more fundamental problem of providing an improved way of formulating a wide range of water insoluble agrochemical or other active ingredients in an economic manner in the form of environmentally satisfactory concentrates that can readily be diluted with water to form sprayable compositions.